Armchair Graphene Nanoribbons (AGNRs) are one-dimensional stripes of graphene with a width-dependent electronic bandgap[1], which makes them suitable for applications in carbon-based nanoelectronics. AGNRs can be effectively produced by on-surface reaction of halogenated bianthracene (DBBA) monomers, a synthesis technique providing atomic control on the dimension and edge structure of the ribbons[2]. Furthermore, the electronic structure of the AGNRs can also be tuned by chemical modification of the precursors.

Here, we report on the properties of 7-AGNRs periodically doped with boron pairs on Au(111). Our density functional theory (DFT) based findings are compared with scanning tunneling microscopy (STM) and angle-resolved photoemission (ARPES) data. We find that the di-boron backbone reduces the band gap of the nanoribbon, and induces the formation of a new conduction band near the Fermi level. Furthermore, it is possible to grow structures formed by pristine segments separated by regions doped with B pairs. We have studied the properties of such boron defects as scattering centers, and found that they provide large effective barriers for the propagation of electrons in the valence band (VB), but are nearly transparent for the immediately lower energy band (VB-1) due to the different symmetry of both bands. As a result, the VB gives rise to clearly identifiable quantized levels in the pristine regions, with a remarkable agreement between theory and experiment[3].